Effects of dietary Bacillus subtilis DSM 32315 supplementation on the growth, immunity and intestinal morphology, microbiota and inflammatory response of juvenile largemouth bass Micropterus salmoides

This study aimed at evaluating the effects of dietary inclusion of Bacillus subtilis DSM 32315 on the growth, immunity, intestinal architecture and gut microbiota of juvenile largemouth bass Micropterus salmoides (LMB). B. subtilis DSM 32315 was supplemented in the diets at the levels of 0 (control, CON), 1.5 (BS1.5, 3 × 106 CFU/g feed) and 3 g/kg (BS3, 6 × 106 CFU/g feed). Each diet was assigned to four replicate tanks of LMB juveniles (initial mean body weight, 8.32 ± 0.06 g) with 20 fish per tank for 9 weeks. The results showed that the growth and feed utilization of LMB were not sensitive to dietary modifications (p > .05). Compared with the CON fish, dietary BS supplementation did not affect the haematological parameters (white and red blood cell counts and haematocrit value) of LMB (p > .05), but the BS1.5 fish performed better than the BS3 fish. Serum innate immunity indicators (lysozyme activity and complement C3 and C4 levels) were improved with dietary BS supplementation at both doses, while higher serum IgM level was only recorded at 1.5 g/kg feed (p